Use libstdc++11 for clang prior to 16.

Clang prior to version 16 does not support libstdc++13 that is installed
by default in GHA image ubuntu 22.04 in C++20 mode.

Update test/Jamfile

Android doesn't support pthread_setcancelstate. Fixes boostorg#150.

Avoid -Wsign-conversion warning in checked_delete.hpp

Add note about identity being moved from functional

Add note about identity being moved from functional

Added missing release notes for Boost 1.80.0.

Updated to GHA checkout@v3 to avoid deprecation warnings.

Add documentation for rebind C++03 compatibility

Update ci.yml